Method of forming a photographic color image

ABSTRACT

A silver halide material can be processed using a redox amplification developer solution and a bleach solution. Both solutions contain a peroxide oxidant.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of application Ser. No. 08/684,897 filedJul. 25, 1996, entitled: Method of Forming A Photographic Color Image.

FIELD OF THE INVENTION

The invention relates to a method of forming a color photographic imageby a redox amplification method. In particular, this invention relatesto processing low silver photographic materials in a redox amplifyingdeveloper followed immediately by a bleach step.

BACKGROUND OF THE INVENTION

Redox amplification processes have been described, for example inBritish Specification Nos. 1,268,126, 1,399,481, 1,403,418 and1,560,572. In such processes, color materials are developed to produce asilver image (which may contain only small amounts of silver) and arethen treated with a redox amplifying solution (or a combineddeveloper-amplifier) to form a dye image.

The developer-amplifier solution contains a color developing agent andan oxidizing agent that will oxidize the color developing agent in thepresence of the silver image which acts as a catalyst.

Oxidized color developer reacts with a color coupler to form the imagedye. The amount of dye formed depends on the time of treatment or theavailability of color coupler and is less dependent on the amount ofsilver in the image as is the case in conventional color developmentprocesses.

Examples of suitable oxidizing agents include peroxy compounds includinghydrogen peroxide and compounds that provide hydrogen peroxide, e.g.,addition compounds of hydrogen peroxide; cobalt (III) complexesincluding cobalt hexammine complexes; and periodates. Mixtures of suchcompounds can also be used.

The image-forming step can be followed by a stop bath, bleach and fix,although the bleach and/or fix may be omitted if the silver coatingweight of the material processed is low enough. Recently it has beenproposed that the bleach bath may contain a peroxide as sole bleachingagent. Such proposals have carried the warning that redox amplificationhas to be stopped before bleaching otherwise color staining will occurdue to image formation continuing in the peroxide bleach solution.

There is a continuing need to reduce photographic processing times. Thisis desirable as it means that processing throughput can be increased.The customer is equally pleased because he can see the results a littlesooner.

SUMMARY OF THE INVENTION

According to the present invention there is provided a method of forminga photographic image comprising:

A) color developing an imagewise exposed photographic silver halidematerial with a redox amplification developer solution comprising anoxidant, and

B) bleaching the material with a bleach solution comprising hydrogenperoxide or a compound that releases hydrogen peroxide duringprocessing, and an alkali metal halide,

wherein step B) follows step A) without an intermediate processing step,and image formation by redox amplification continues during bleaching.

According to this invention, the processing time can be reduced while atthe same time better colors are obtained. The effluent from the processcontains no iron as it would if a conventional ferric EDTA bleachingagent were used. The overall chemical oxygen demand of the process isreduced. Without the alkali metal halide in the bleach solution theemulsion layers of the treated material are destroyed by the formationof oxygen bubbles. In addition, stain is formed without the halide.

Preferably the time of bleaching in the present invention is less thanthe time used for the devamp step. Particularly, the bleach time is lessthan one-half the time for the devamp step, and more preferably, thebleaching time is one-third or less than the time of the devamp step.

DETAILED DESCRIPTION OF THE INVENTION

Preferably the oxidant of the redox amplification step is hydrogenperoxide or a compound that releases hydrogen peroxide duringprocessing.

The present bleach solutions preferably contain an alkali metal halideat a concentration of 0.25 to 50 g per liter, preferably 0.5 to 35 g perliter, more preferably 1 to 30 g per liter. In the absence of halide thebleach solution forms oxygen bubbles in the material being processed andremoves the emulsion layers of the material from the support.

The present bleach baths preferably contain 30% hydrogen peroxide atconcentrations of from 10 to 300 ml/l, preferably from 20 to 100 ml/l(when provided as a 30% solution). Preferably hydrogen peroxide is thesole oxidant of the bleach.

The present bleach baths preferably have a pH of from 8 to 11.5,preferably from 9 to 11.

A particular application of this technology is in the processing ofsilver chloride color paper, for example paper whose silver halidecomprises at least 85 mole percent silver chloride, especially suchpaper with low silver levels, for example silver levels below 30 mg/m²,preferably below 20 mg/m², especially within the range of 1 to 20 mg/m².

The photographic materials can be black-and-white, single color elementsor multicolor elements. Multicolor elements contain dye image-formingunits sensitive to each of the three primary regions of the spectrum.Each unit can be comprised of a single emulsion layer or of multipleemulsion layers sensitive to a given region of the spectrum. The layersof the element, including the layers of the image-forming units, can bearranged in various orders as known in the art. In an alternativeformat, the emulsions sensitive to each of the three primary regions ofthe spectrum can be disposed as a single segmented layer.

A typical multicolor photographic element comprises a support bearing acyan dye image-forming unit comprised of at least one red-sensitivesilver halide emulsion layer having associated therewith at least onecyan dye-forming coupler, a magenta dye image-forming unit comprising atleast one green-sensitive silver halide emulsion layer having associatedtherewith at least one magenta dye-forming coupler, and a yellow dyeimage-forming unit comprising at least one blue-sensitive silver halideemulsion layer having associated therewith at least one yellowdye-forming coupler. The element can contain additional layers, such asfilter layers, interlayers, overcoat layers, subbing layers, and thelike.

Suitable materials for use in the emulsions and elements processed bythe method of this invention, are described in Research Disclosure Item36544, September 1994, published by Kenneth Mason Publications,Emsworth, Hants, United Kingdom.

The present processing method is preferably carried out by passing thematerial to be processed through a tank containing the processingsolution that is recirculated through the tank at a rate of from 0.1 to10 tank volumes per minute.

The method of this invention is generally carried out using a redoxamplification dye image-forming or devamp step of from about 15 to about120 seconds, and preferably for from about 20 to about 60 seconds. Thebleach step is generally at least about 5 seconds, with a time of fromabout 7 to about 20 seconds being preferred. As noted above, it ispreferred that the bleach step be less than one-half the time for thedevamp step, and more preferably, that it is one-third or less of thedevamp time.

The preferred recirculation rate is from 0.5 to 8, especially from 1 to5 and particular from 2 to 4 tank volumes per minute.

The recirculation, with or without replenishment, is carried outcontinuously or intermittently. In one method of working both could becarried out continuously while processing was in progress but not at allor intermittently when the machine was idle. Replenishment may becarried out by introducing the required amount of replenisher into therecirculation stream either inside or outside the processing tank.

It is advantageous to use a tank of relatively small volume. Hence in apreferred embodiment of the present invention the ratio of tank volumeto maximum area of material accommodatable therein (i.e., maximum pathlength×width of material) is less than 11 dm³ /m², preferably less than3 dm³ /m².

The shape and dimensions of the processing tank are preferably such thatit holds the minimum amount of processing solution while still obtainingthe required results. The tank is preferably one with fixed sides, thematerial being advanced therethrough by drive rollers. Preferably thephotographic material passes through a thickness of solution less than11 mm, preferably less than 5 mm and especially about 2 mm. The shape ofthe tank is not critical but it could be in the shape of a shallow trayor, preferably U-shaped. It is preferred that the dimensions of the tankbe chosen so that the width of the tank is the same or only just widerthan the width of the material to be processed.

The total volume of the processing solution within the processingchannel and recirculation system is relatively smaller as compared toprior art processors. In particular, the total amount of processingsolution in the entire processing system for a particular module is suchthat the total volume in the processing channel is at least 40 percentof the total volume of processing solution in the system. Preferably,the volume of the processing channel is at least about 50 percent of thetotal volume of the processing solution in the system.

In order to provide efficient flow of the processing solution throughthe opening or nozzles into the processing channel, it is desirable thatthe nozzles/opening that deliver the processing solution to theprocessing channel have a configuration in accordance with the followingrelationship:

    0.6≦F/A≦23

wherein:

F is the flow rate of the solution through the nozzle in liters/minute;and

A is the cross-sectional area of the nozzle provided in squarecentimeters.

Providing a nozzle in accordance with the foregoing relationship assuresappropriate discharge of the processing solution against thephotosensitive material. Such Low Volume Thin Tank systems and methodsof use are described in more detail in the following patentspecifications: U.S. Pat. Nos. 5,294,956, 5,179,404, 5,436,118,5,270,762, EP 559,025, EP 559,026, EP 559,027, WO 92/10790, WO 92/17819,WO 93/04404, WO 92/17370, WO 91/19226, WO 91/12567, WO 92/07302, WO93/00612, WO 92/07301, and WO 92/09932.

The following Example is included for a better understanding of theinvention.

EXAMPLE

The following processing solutions were made up.

    ______________________________________    RX developer/amplifier    1-hydroxyethylidene-1,1'-diphosphonic                          0.6      g    acid    diethyltriaminepentaacetic                          2.0      g    acid    Dipotassium hydrogen phosphate                          40.0     g    Hydroxylamine sulfate 0.5      g    4-N-ethyl-N-(β-methanesulfonamido-                          4.5      g    ethyl)-o-toluidine sesquisulfate    Hydrogen Peroxide (30%)                          2        ml    Water to              1        liter    pH adjusted to 11.7    Fix/stop    Sodium thiosulfate pentahydrate                          20       g    Sodium sulfite anhydrous                          30       g    Sodium acetate        40       g    Water to              1        liter    pH adjusted to 5.0    with sulfuric acid at 25° C.    Bleach-fix    Sodium iron(III) EDTA 75       g    Sodium thiosulfate pentahydrate                          75       g    Acetic acid           10       ml    Water to              1        liter    pH adjusted to 6.0 at 20° C.    with 10% sodium carbonate solution    Bleach 1    30% hydrogen peroxide 50       ml    sodium chloride       1        g    sodium hydrogen carbonate                          20       g    Water to              1        liter    pH adjusted to 10.0 at 20° C.    with 3 molar sodium hydroxide    Bleach 2    30% hydrogen peroxide 50       ml    sodium hydrogen carbonate                          20       g    Water to              1        liter    pH adjusted to 10.0 at 20° C.    with 3 molar sodium hydroxide    ______________________________________

The solutions described above were use to process a low silver papercontaining 19 mg Ag/m² in red and green sensitive layers and 30 mg Ag/m²in the blue sensitive layer, exposed to 21 step color wedges for 0.1sec. The processes carried out were as follows:

    ______________________________________    Process 1 (Comparison)    Develop         45 sec  35° C.    Fix/Stop        45 sec  35° C.    Bleach-Fix      45 sec  35° C.    Wash            45 sec  35° C.    Dry    Process 2 (Comparison)    Develop         45 sec  35° C.    Fix/Stop        45 sec  35° C.    Wash            45 sec  35° C.    Dry    Process 3 (Invention)    Develop         35 sec  35° C.    Bleach 1        10 sec  35° C.    Fix/Stop        45 sec  35° C.    Wash            45 sec  35° C.    Dry    Process 4 (Comparison)    Develop         35 sec  35° C.    Bleach 2        10 sec  35° C.    Fix/Stop        45 sec  35° C.    Wash            45 sec  35° C.    Dry    Process 5 (Comparison)    Develop         35 sec  35° C.    Fix/Stop        45 sec  35° C.    Wash            45 sec  35° C.    Dry    ______________________________________

After processing, the steps were read and sensitometric parameterscalculated.

The following Table 1 summarizes the sensitometry read on the neutralexposed wedge.

                                      TABLE 1    __________________________________________________________________________    Process        Dmin     Dmax     Speed    Inertia Speed    No. R  G  B  R  G  B  R  G  B  R  G  B    __________________________________________________________________________    1   .095           .101              .086                 2.95                    2.66                       2.29                          133                             123                                125                                   150                                      144                                         151    2   .097           .104              .088                 2.91                    2.71                       2.53                          137                             129                                130                                   153                                      147                                         154    3   .101           .104              .086                 2.90                    2.66                       2.28                          142                             131                                129                                   162                                      154                                         160    4   .143           .125              .120                 -- -- -- -- -- -- -- -- --    5   .092           .092              .082                 2.61                    2.46                       1.81                          129                             119                                119                                   148                                      142                                         147    __________________________________________________________________________             Process                 Contrast Shoulder Contrast                                   Toe             No. R  G  B  R  G  B  R  G  B    __________________________________________________________________________             1   4.83                    3.79                       3.08                          2.27                             2.01                                1.76                                   .196                                      .229                                         .228             2   4.81                    4.23                       3.47                          2.23                             2.09                                1.89                                   .196                                      .238                                         .235             3   4.65                    4.07                       3.16                          2.17                             2.01                                1.84                                   .197                                      .230                                         .230             4   -- -- -- -- -- -- .214                                      .253                                         .241             5   4.24                    3.65                       2.86                          1.99                             1.85                                1.55                                   .192                                      .223                                         .221    __________________________________________________________________________

The results show that the sensitometry of the invention, Process 3, issimilar to the bleach-fixed process but took 45 seconds less time toprocess. Process 2 shows increased density and contrast due to retainedsilver. The sensitometry of Process 4 was not complete as the paper wasdestroyed in high density area by the formation of oxygen bubbles in thefilm. At low densities without chloride in the bleach, stain wasobserved. The shorter development time (35 sec) without the bleachfollowing the developer showed low density particularly in the bluesensitive layer, demonstrating that formation of the dye image wascontinuing in the bleach

The following Table 2 summarizes the Dmin and Dmax read on the blueexposed wedge. This shows the amount unwanted color contamination due toretained silver.

                  TABLE 2    ______________________________________           Dmin         Dmax    Process No.             R      G        B    R      G    B    ______________________________________    1        0.089  0.098    0.084                                  0.14   0.54 2.20    2        0.094  0.104    0.091                                  0.28   0.68 2.31    3        0.090  0.102    0.085                                  0.16   0.57 2.20    4        0.143  0.120    0.121                                  --     --   --    5        0.087  0.098    0.082                                  0.27   0.69 2.12    ______________________________________

In the Dmax area of Processes 2 and 5 without bleach (comparative) highred and green densities are observed in the blue exposed patches due toretained silver that results in color degradation of the yellow layerparticularly at high densities. Most of this increased gray density isremoved by process 3 (the invention), in which the result is similar tothe long process time Process 1 (comparative). Processes 1 and 3 give`brighter` yellows.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

I claim:
 1. A method of forming a photographic image comprising:A) colordeveloping an imagewise exposed photographic silver halide material witha redox amplification developer solution comprising an oxidant, and B)bleaching said material with a bleach solution comprising hydrogenperoxide or a compound that releases hydrogen peroxide duringprocessing, and an alkali metal halide, wherein step B) follows step A)without an intermediate processing step, and image formation by redoxamplification continues during bleaching, and wherein the time forbleaching step B is one-third or less than the time for devamp step A.2. The method of claim 1 wherein said oxidant in said developer solutionis hydrogen peroxide or a compound which releases hydrogen peroxideduring processing.
 3. The method of claim 1 wherein said bleach solutioncontains said alkali metal halide at a concentration of from 0.25 to 50g per liter.
 4. The method of claim 3 wherein said bleach solutioncontains said alkali metal halide at a concentration of from 0.5 to 35 gper liter.
 5. The method as claimed in any of claim 1 wherein saidbleach solution has a pH of from 9 to
 11. 6. The method of claim 1wherein said photographic silver halide material is a silver chloridecolor paper comprising a silver halide emulsion comprising at least 85mole percent silver chloride.
 7. The method of claim 6 wherein the totalsilver halide coverage in said photographic material is less than orequal to 30 mg/silver per m².
 8. The method of claim 7 wherein the totalsilver halide coverage is from 1 to 20 mg silver per m².
 9. The methodof claim 1 carried out by passing said material through a tankcontaining either said developer or bleach solution that is recirculatedthrough said tank at a rate of from 0.1 to 10 tank volumes per minute.10. The method of claim 1 carried out in a processing machine whereinthe ratio of tank volume to maximum area of material accommodatabletherein is less than 11 dm³ /m².
 11. The method of claim 10 wherein theratio of tank volume to maximum area of material accommodatable thereinis less than 3 dm³ /m².
 12. The method of claim 1 wherein said bleachsolution comprises 10 to 300 ml hydrogen peroxide (30%) per liter. 13.The method of claim 9 wherein either said developer or bleach solutionis recirculated through said tank at a rate of from 0.5 to 8 tankvolumes per minute.